1. Field of the Invention
The present invention relates to a method and apparatus for providing enhanced Ethernet path selection using optical levels.
2. Description of Related Art
Telcos or large carriers such as AT&T and Verizon, which can provide telecommunications and data communications services to customers throughout large geographic areas, are increasingly using Ethernet but still support significant SONET infrastructure. Telcos want to provide Carrier Ethernet with the same quality of service (QoS) as SONET QoS. Unlike service providers for Enterprise Ethernet networks (e.g., in buildings, and on campuses), these telcos or larger carriers are accustomed to using SONET metrics such as bit error rate (BER) of SONET payload for path degradation detection. Unlike SONET, however, Ethernet transmission has no meaningful BER metric. For example, Ethernet packets vary significantly and, as such, their degradation or loss does not correlate accurately to a BER, yet packet loss can be significant. Further, unlike Enterprise Ethernet providers, telcos are required to guarantee a level of QoS to customers for SONET as well as any Ethernet service they provide. A need therefore exists for convenient employment of a more accurate QoS metric for larger carrier Ethernet transport.
For telcos or large carriers providing Carrier Ethernet, a need also exists for protection switching to occur as quickly as possible and with the lowest errors possible. For example, many fiber optic Ethernet devices that support redundant or aggregated data paths employ Loss of Signal (LOS) to indicate a failing data path and, accordingly, a need to switch to alternate data path(s). Existing Ethernet devices, however, are disadvantageous because excessive errors may occur on the failing data path before LOS occurs in the event of seriously degraded fiber optic performance.
Ethernet path selection can occur, for example, in the context of Ethernet Automatic Protection Switching (APS) (e.g., as defined in Recommendation ITU-T G.8031 for linear 1:1 or 1+1 protection switching mechanism for VLAN-based Ethernet networks). G.8031 supports 1:1 linear protection through implementation of point-to-point Ethernet Tunnels providing a working and protecting Ethernet circuit, where the path providing the protection is always available through health-monitoring.
Within each working and protecting Ethernet circuit or path, using fast Connectivity Check Messages (CCM) can provide an inherent fault detection mechanism as part of the protocol since they are used to verify basic service connectivity and health of data paths. Failure detection of a working path by such a mechanism can trigger a move from working to protecting circuits. Upon failure, re-convergence times are dependent on the failure detection mechanisms. For example, the CCM transmit interval can determine the response time. The OS supports message timers as low as 10 milliseconds so the restoration times are comparable to SONET/SDH. Alternatively, 802.3ah (Ethernet in the First Mile) or simple Loss of Signal can act as a trigger for a protection switch where appropriate.
If a failure of a link or node affects the working or primary Ethernet tunnel path, the services will fail to receive the CCMs exchanged on that path or will receive a fault indication (e.g., LOS) from the link layer OAM module. Network equipment (NE) declares connectivity failure when a designated number of consecutive CCMs (e.g., three) are lost. For example, when a path has degraded but has not completely failed, one in four CCMs may be received, leaving 75% of the data being possibly in error and with no alarm message or declaration of path failure. Thus, degraded path conditions continue to occur.
Further, a LOS signal is not generated or asserted until a designated optical level (e.g., −x dbm) parameter or condition is met. As with the absence of consecutive CCMs, an optical path can be operating under degraded conditions long before received optical signal level meets the designated level for asserting LOS.
A need therefore exists for a prompt mechanism for determining if an optical path has degraded. Also, a need exists for shortening the time interval between the detection or indication of possible Ethernet path degradation and the initiation of Ethernet path selection (e.g., switch protection). A need also exists for a method or apparatus that determines inadequate receive level in an Ethernet path and generates a LOS or other fault or alarm indication as early as possible after signal degradation commences (e.g., even before the designated level for asserting LOS in a particular SFP is met).